#' Flat theme for highcharts
#'
#' Flat and flatdark theme is inspired by 
#' \url{https://github.com/chriskempson/base16} and
#' \url{https://github.com/cttobin/ggthemr#flat}
#' 
#' @param ... A named parameters to modify the theme.
#' 
#' @examples
#'
#' highcharts_demo() %>%
#'   hc_add_theme(hc_theme_flat())
#' @export
hc_theme_flat <- function(...) {
  theme <-
    list(
      colors = c(
        "#f1c40f", "#2ecc71", "#9b59b6", "#e74c3c",
        "#34495e", "#3498db", "#1abc9c", "#f39c12", "#d35400"
      ),
      chart = list(
        backgroundColor = "#ECF0F1"
      ),
      xAxis = list(
        gridLineDashStyle = "Dash",
        gridLineWidth = 1,
        gridLineColor = "#BDC3C7",
        lineColor = "#BDC3C7",
        minorGridLineColor = "#BDC3C7",
        tickColor = "#BDC3C7",
        tickWidth = 1
      ),
      yAxis = list(
        gridLineDashStyle = "Dash",
        gridLineColor = "#BDC3C7",
        lineColor = "#BDC3C7",
        minorGridLineColor = "#BDC3C7",
        tickColor = "#BDC3C7",
        tickWidth = 1
      ),

      legendBackgroundColor = "rgba(0, 0, 0, 0.5)",
      background2 = "#505053",
      dataLabelsColor = "#B0B0B3",
      textColor = "#34495e",
      contrastTextColor = "#F0F0F3",
      maskColor = "rgba(255,255,255,0.3)"
    )

  theme <- structure(theme, class = "hc_theme")

  if (length(list(...)) > 0) {
    theme <- hc_theme_merge(
      theme,
      hc_theme(...)
    )
  }

  theme
}
